Instrument rating refers to the qualifications that a pilot must have in order to fly under instrument flight rules (IFR). It requires additional training and instruction beyond what is required for a private pilot certificate or commercial pilot certificate, including rules and procedures specific to instrument flying, additional instruction in meteorology, and more intensive training in flight solely by reference to instruments. Testing consists of a written exam and a practical test (known more commonly as the check ride). The check ride is divided into an oral component to verify that the applicant understands the theory of instrument flying and an actual flight to ensure the pilot possesses the practical skills required for safe IFR flight.
The modern aircraft has the abilities to fly in high altitude, rough weather and low visibility provided the pilots have the required trainings and endorsements too.